Asphalt, or bitumen, is commonly collected or synthesized and refined for use in paving and roofing applications. The type of asphalt suitable for paving applications is commonly referred to as “paving grade asphalt,” or “paving asphalt,” or “asphalt cement.” Asphalt suitable for roofing applications is commonly referred to as “roofing flux,” “flux asphalt,” or simply “flux.” In general, paving asphalt is harder than roofing flux. In fact, roofing flux is initially too soft to be used, especially for roofing shingle manufacturing. Rather, a process called “air blow,” or “oxidation,” is applied to roofing flux to make it harder and, therefore, more suitable for roofing applications. The product of such air blow processes is called “blown coating” or “oxidized asphalt” or “oxidized bitumen” and is suitable for use to make roofing products, such as roofing shingles.
For roofing applications, oxidized flux asphalt may be applied directly to a roof structure, and aggregate spread over and pressed into the asphalt to form a built up roof. Alternatively, flux asphalt or oxidized flux asphalt may be coated onto fiberglass, polyester or other sheet-like material to form a membrane or shingle. Inorganic filler such as mineral filler may also be mixed into the flux asphalt or oxidized flux asphalt for roofing applications. Additional components such as recycled material, performance additives, or combinations thereof, may be added to the asphalt.
The strength and durability of asphalt materials depend on various factors including the properties of the materials used and the environmental conditions to which the asphalt material is exposed. Conventional asphalt materials suffer from various drawbacks due to exposure to environmental conditions, such as, for example, developing oil bleeding. Oil bleeding can affect adhesion between waterproof membranes and between the waterproof membrane and building decks. Oil bleeding can also display as surface oil stains, which are aesthetically undesirable to end users. Also there is a tendency, in hot weather when the asphalt roofing product does not have sufficient heat resistance, for the surface and/or the back coating layer of an installed asphalt product to soften and slide, thereby leaving portions of the roof unprotected.
To improve resistance of asphalt materials to these and other problems, various materials may be added to asphalt compositions before use in roof products. For example, high temperature performance additives, e.g., plastomers and/or elastomers, and/or low temperature performance additives, e.g., process oils, may be incorporated into the asphalt materials. The high temperature performance additives tend to increase the modulus of the asphalt material at higher temperatures to resist permanent deformation and creep, while the low temperature performance additives tend to increase flexibility and ductility of the asphalt material at lower temperatures to resist brittleness and cracking. While the roofing industry continues its efforts to develop a balance between these two categories of additives, sliding of roof products continues to be a challenge for the roofing industry. In addition, neither type of additive addresses the need for oil bleeding resistance.
Accordingly, it is desirable to provide asphalt compositions for producing roofing products with improved oil bleeding resistance and increased heat resistance. It also is desirable to provide methods for making such asphalt compositions. In addition, it is desirable to provide filled asphalt materials comprising such asphalt compositions. Additional beneficial features and characteristics of the asphalt compositions will become apparent from the subsequent detailed description and examples.